The present invention relates to imaging apparatuses having an imaging element, which are used for electronic still cameras, digital cameras and the like. More particularly, the present invention relates to an imaging apparatus having an imaging element for accumulating signal charge corresponding to an incident scene light flux in a photo-electric converting element section and transferring the accumulated signal charge through a vertical shifter to a horizontal shifter so as to be read out therefrom, and a shutter means for selectively blocking the scene light flux to be incident on the imaging element.
Hitherto, various imaging apparatuses have been proposed as a digital still camera and a digital camera. The imaging elements applicable to such imaging apparatuses have also been proposed. Among such imaging elements is an inter-line CCD solid-state imaging element having a vertical overflow drain structure as schematically shown in FIG. 14.
The CCD shown in FIG. 14 comprises a two-dimensional array of photo-diodes 1 arranged in both horizontal and vertical directions and each constituting a photo-electric converting cell for accumulating charge according to light incidence, a plurality of vertical shift registers 3 constituting vertical shift paths for receiving charge accumulated in associated photo-diodes 1 via a transfer gate 2 and progressively vertically shifting the received charge, a horizontal shift register 4 constituting a horizontal shift path for receiving shifted charge from the vertical shift registers 3 and progressively horizontally shifting the received charge, and a signal detector 5 for amplifying the output signal of the horizontal shift register 4 and outputting the amplified signal.
FIG. 15 is a block diagram showing the construction of a prior art imaging apparatus with the CCD shown in FIG. 14. The illustrated imaging apparatus comprises a focusing lens 11, a shutter means 12, a CCD 13, as a signal processor 14, a shutter driver 16, a signal generator 17, and a CPU 18. The focusing lens 11 focuses a light beam of a scene on a light incidence surface of the CCD 13. The shutter means 12 is constituted by, for instance, a mechanical shutter for either passing or blocking the scene light flux. The CCD 13 converts the scene light beam flux having passed through the shutter means 12 to an electric signal. The signal processor 14 performs various processes on the electric signal from the CCD 13 and outputs an image signal thus generated. The shutter driver 16 controls the shutter means 12. The signal generator 17 supplies pulses for controlling the period of charge accumulation in the photo-diodes 1, pulses for driving the vertical shift registers 3 and pulses for driving the horizontal shift register 4 and also supplies pulses for driving the signal processor 14 in synchronism with the CCD 13. The CPU 18 collectively controls circuits including the driver 16 and signal generator 17. The signal processor 14 and the signal generator 17 together constitute a digital signal processor (DSP) 19.
FIG. 16 is a timing chart illustrating a conventional imaging operation in the imaging apparatus shown in FIG. 15. Specifically, the Figure shows a vertical sync signal VD, a transfer gate pulse train TG, a sub-pulse train SUB, a vertical shift register shift pulse train VT, a clamp pulse train CLP, opening/closing operation of the shutter means 12, and a CCD signal, i.e., a signal read out from the CCD 13.
The vertical sync signal VD is a pulse train prescribing a predetermined unit period of time for obtaining a signal representing one image (i.e., one frame image). Here, periods prescribed by the individual pulses are labeled V1, V2, . . . .
The transfer gate pulse train TG consists of pulses for determining the timing of the transfer of charged stored in the photo-diodes 1 to the vertical shift registers 3, and is applied to the transfer gate 2 in synchronism with the vertical sync signal VD. The transfer gate pulses TG corresponding to the periods, V1, V2, . . . of the vertical sync signal VD are labeled TG0, TG1, . . . .
The sub-pulse train SUB consists of pulses for discharging charge generated in the photo-diodes 1 in the vertical direction of the substrate. The charge discharge is done while sub-pulses SUB are outputted. That is, the charge is accumulated in the photo-diodes 1 during periods tb1, tb2, . . . in which the sub-pulses SUB are stopped in the periods V1, V2, . . . of the vertical sync signal VD. Thus, it will be seen that a so-called element shutter is realized, in which the effective exposure time is controlled through control of the charge accumulation period. The charge accumulation time is determined as a result of measurement of light of the scene image with a measuring means (not shown), and it is measured by counting sub-pulses SUB.
The vertical shift register shift pulse train VT consists of pulses for causing progressive shift of charge in the vertical shift registers 3 toward the horizontal shift register 4.
The clamp pulse train CLP consists of pulses for clamping the CCD signal corresponding to an optical black portion of the CCD. By the clamping, the potential level of the image signal is stabilized to hold a stable black level.
The shutter means 12 is normally open, and is closed (light-shuttered or -blocked) when causing the transfer of charge accumulated in the photo-diodes 1 in response to a recording trigger signal. As the recording trigger signal, in the case of a shutter release button (not shown) providing a two-stage trigger signal, that is, in the case when a first trigger pulse is generated in a preparatory stage of lightly depressing the shutter release button for AF locking and a second trigger pulse is generated by further depressing the shutter release button for starting the recording of a still image, the second trigger pulse corresponds to the recording trigger signal.
The CCD signal has time sections to1 and to2 corresponding to optical black portions in the vertical direction and an effective time section intervening as a scene image period between these time sections. Normally the optical black signal is at a higher level than the effective period signal level.
As is seen from the timing chart of FIG. 16, in the prior art imaging apparatus upon generation of a recording trigger signal in, for instance, the period V3, vertical shift register shift pulses VT are continuously outputted during a subsequent time section ta for fast sweep-out of unnecessary charge in the vertical shift registers 3. In the subsequent period V4, the charge is accumulated in the photo-diodes 1 by suspending the application of sub-pulses SUB for a time section tb4 corresponding to the exposure period, which has been determined on the basis of the CCD signal until the recording trigger signal generation. Accordingly, the time section tb4 constitutes an exposure time for one frame image.
In the subsequent period V5, the image obtained by the exposure during the time section tb4 in the period V4 is outputted as signal CCD4, which is outputted as a result of the exposure in response to the recording trigger signal from the signal amplifier 5. Also, in synchronism with the start of the period V5, the shutter driver 16 is caused to drive the shutter means 12 for closing and in the subsequent period v6 the shutter means 12 is opened. The image obtained by exposure as a result of the closing operation of the shutter means 12 in the period V5, is outputted as signal CCD5 in the subsequent period V6. Since the signal CCD5 is obtained while the shutter means is blocking incident light, the signal levels in the optical black portion time sections and the effective period are substantially equal.
As shown above, in the prior art imaging apparatus, fast sweep-out of charge from the vertical shift registers 3 is performed in the period V3. The light-blocking operation of the shutter means 12 is performed so as to cause the charge accumulation in the photo-diodes 1 during the time section tb4 in the period V4, and cause the transfer of the accumulated charge in the subsequent period V5, and the shutter means 12 is opened again in the subsequent period V6.
In the above prior art imaging apparatus, however, a response time tm is required from the start of the closing operation of the shutter means 12 until the perfectly closed state is brought about. In other words, even with the closing operation started at the start of the charge transfer period V5, during the response time tm the light is incident on the CCD 13, resulting in charge generation in the photo-diodes 1. Therefore, particularly in case of a bright scene the charge generated during the response time tm partly enters the vertical shift registers 3 in spite of the charge sweep-out in the vertical direction with sub-pulses SUB. Also, the generated charge remains on the substrate part of the photo-diodes 1, and is shifted by the vertical shift registers 3 after the shutter means 12 has been perfectly closed. Thus, a problem of the superimposition of smear on the intrinsic CCD signal is posed.
To solve the problem noted above, the applicant has earlier proposed an imaging apparatus , which has the structure as shown in FIG. 15, and in which the imaging operation is controlled with timings as shown in FIG. 17 (Japanese Patent Application No. 8-344052). In this imaging apparatus, after the recording trigger pulse generation the fast sweep-out of unnecessary charge in the vertical shift registers 3 is done in a time section tc in synchronism with transfer gate pulse TG3 synchronized to the vertical sync signal VD. The vertical shift register shift pulse VT for the fast sweep-out period tc need not be synchronized to the horizontal blanking period because of the fact that unnecessary charge which is not used as data is swept out.
Transfer gate pulse TG4 prescribes the end instant of the fast sweep-out period tc, and also causes transfer of signal charge having been accumulated during the charge accumulation time section tb4 to the vertical shift registers 3. The timing of generation of the pulse TG4 is fixedly set such that it is earlier than the start of the next period V5 by a predetermined time interval tv, which is determined on the basis of the response time tm of the shutter means 12 and an allowance thereof. The shutter means 12 starts the light-blocking in synchronism with the transfer gate pulse TG4.
Furthermore, the vertical shift of the signal charge transferred to the vertical shift registers 3, is suspended for a predetermined time tv, and the read-out is started by starting the application of vertical shift register shift pulses VT in synchronism with this vertical shift suspension time tv, i.e., with the start of the next period V5. The timing of the start of the charge accumulation time section tb4 after the generation of the recording trigger signal, is determined to be earlier than the timing of generation of the transfer gate pulse TG4 by the charge accumulation time section tb4.
With the imaging apparatus as described, the shutter means 12 can be in the perfectly closed state in the period V5, in which the signal charge accumulated during the charge accumulation time section tb4 in the period V4 is read out. It is thus possible to solve the above problem of smear and obtain high quality image signal.
However, by various researches and investigations conducted by the inventors, it was revealed that the imaging apparatus proposed by the applicant has a problem to be solved as will be described hereinunder.
Specifically, the motion of the shutter means 12 is degraded or slow due to the following:
(1) The shutter means 12 constituted of, for instance, mechanical shutter provides a slow moving operation at low temperature.
(2) The shutter means 12 with posture thereof, that is, directing upward or downward provides a slow moving operation due to increase in friction of moving member of the shutter means 12.
(3) The driving means of the shutter means 12 provides a slow moving operation due to the reduction of the power source (for instance, battery) voltage level.
(4) Deterioration with age provides a slow moving operation. As a result, even if the vertical transfer suspension time tv is set on the basis of the normal response time tm and an allowance thereof, according to the operation conditions such as ambient temperature, posture, power source voltage level, or changes with age, the response time tmxe2x80x2 is longer than the vertical transfer suspension time tv as shown in FIG. 17. Accordingly, the shutter means can not perform perfect light-block operation even if the vertical transfer by the vertical shift register transfer pulse VT is started, causing the same problems as in the prior art.
Such a problem is posed not only in the case of constructing the shutter means 12 with a mechanical shutter but also in the case with a liquid crystal shutter. The liquid crystal shutter has a response characteristic which is dependent on temperature and also on applied voltage and also subject to deterioration with age. Therefore, the above problem is posed depending on operating conditions.
The present invention seeks to solve the above problem, and its object is to provide an imaging apparatus capable of providing a high quality image signal free from smear to be always obtained from the imaging element.
According to a first aspect of the present invention, there is provided an imaging apparatus having an imaging element for accumulating signal charge corresponding to an incident scene light flux in a photo-electric converting element section and transferring the accumulated signal charge through a vertical shifter to a horizontal shifter so as to be read out therefrom, and a shutter means for selectively blocking the scene light flux to be incident on the imaging element, comprising: an operating condition judging means for judging the operating condition of the imaging apparatus; and a control means for controlling the imaging operation according to the output of the operating condition judging means.
The control means controls the timing of reading out the signal charge from the imaging element from the instant of start of the light-blocking operation of the shutter means.
The control means controls a vertical shift suspension time from the instant of start of the light-blocking operation till the instant of start of shifting in the vertical shifter of the imaging element according to the output of the operating condition judging means.
The vertical shift suspension time is at least a time from the instant of start of the light-blocking operation of the shutter means till the instant when the perfectly light-blocking state of the shutter means is brought about.
The control means controls a time from the instant of transfer of signal charge from the photo-electric converting element section to the vertical shifter of the imaging element till the instant of start of vertical shifting in the vertical shifter on the basis of the output of the operating condition judging means.
The control means controls the timing of starting the light-blocking operation of the shutter means with respect to a vertical sync signal prescribing unit time of obtaining image signal representing one frame image from the imaging element on the basis of the output of the operating condition judging means.
The control means controls the timing of transferring signal charge from the photo-electric converting element section to the vertical shifter with respect to a vertical sync signal prescribing a unit time of obtaining an image signal of one frame image from the imaging element on the basis of the output of the operating condition judging means.
The control means controls the accumulation operation timing of the signal charge corresponding to the scene light flux in the photo-electric converting element section to the vertical shifter with respect to a vertical sync signal prescribing a unit time of obtaining an image signal of one frame image from the imaging element on the basis of the output of the operating condition judging means.
The operating condition judging means judges the ambient temperature as the operating condition of the imaging apparatus.
The control means controls the time from the instant of start of the light-blocking operation of the shutter means till the read-out of the signal charge from the imaging element on the basis of the result of judgment of the ambient temperature in the operating condition judging means such that the time is the longer the lower the ambient temperature.
The operating condition judging means judges the posture of the imaging apparatus as the operating condition thereof.
The control means controls the time from the instant of start of the light-blocking operation of the shutter means till the read-out of the signal charge from the imaging element according to the result of judgment of the posture of the imaging apparatus in the operating condition judging means such that the time is increased the more the imaging apparatus is tilted from a normal state thereof.
The operating condition judging means judges the power supply voltage level as the operating condition of the imaging apparatus.
The control means controls the time from the instant of start of the light-blocking operation of the shutter means till the read-out of the signal charge from the imaging element on the basis of the result of judgment of the power supply voltage level in the operating condition judging means such that the time is increased the lower the power supply voltage level.
The operating condition judging means judges the number of times of operation of the shutter means as the operating condition of the imaging apparatus.
The control means controls the time from the instant of start of the light-blocking operation of the shutter means till the read-out of the signal charge from the imaging element according to the result of judgment of the shutter means operation times number in the operating condition judging means such that the time is increased the greater the operation times number.
According to another aspect of the present invention, there is provided an imaging apparatus having an imaging element for accumulating signal charge corresponding to an incident scene light flux in a photo-electric converting element section and transferring the accumulated signal charge through a vertical shifter to a horizontal shifter so as to be read out therefrom, and a shutter means for selectively blocking the scene light flux to be incident on the imaging element, comprising: an operating condition judging means for judging the operating condition of the imaging apparatus; and a control means for controlling the imaging operation condition of the imaging apparatus; and a control means for controlling operation timings of the shutter means.
According to other aspect of the present invention, there is provided an imaging apparatus having an imaging element for accumulating signal charge corresponding to an incident scene light flux in a photo-electric converting element section and transferring the accumulated signal charge through a vertical shifter to a horizontal shifter so as to be read out therefrom, and a shutter means for selectively blocking the scene light flux to be incident on the imaging element, comprising: an operating condition judging means for judging the operating condition of the imaging apparatus; and a control means for controlling operation timings of the imaging element.
The operating condition judging means judges as the operating condition of the imaging apparatus at least one of the ambient temperature, the posture of the imaging apparatus, the power supply voltage level and the number of times of operation of the shutter means.
The above as well as other objects and features will be clarified from the following description with reference to attached drawings.